Periodic Reporting for period 4 - NanoFab2D (Novel 2D quantum device concepts enabled by sub-nanometre precision nanofabrication)
Reporting period: 2021-01-01 to 2021-06-30
Nanotechnology reached a point where we are able to study and modify the structure of materials with close to atomic precision. This opens up entirely new possibilities. We develop novel nanofabrication techniques that are able to modify the structure of materials at or even below the nanometer scale. We apply these methods to a recently discovered new class of materials: two-dimensional (2D) crystals, including but not limited to graphene. The central question of our research is: how can we impart novel functionalities to materials through nanometer precision engineering of their structure?
The available materials and technologies determine our potential for further improving existing applications as well as enabling novel applications. New or improved functionality can result in electronic circuits with ultra-high operation speed and ultra-low power consumption increasing our data processing capability while decreasing the energy consumption, which constitutes a growing problem. Moreover, nanometer scale modification of 2D materials can bring substantial improvement in various applications other than electronics, from advanced sensors to more efficient catalysts.
The overall objective of the project is to develop novel device concept, demonstrate new or improved functionality of graphene and other 2D materials through the nanoscale and atomic level engineering of their structure.
The available materials and technologies determine our potential for further improving existing applications as well as enabling novel applications. New or improved functionality can result in electronic circuits with ultra-high operation speed and ultra-low power consumption increasing our data processing capability while decreasing the energy consumption, which constitutes a growing problem. Moreover, nanometer scale modification of 2D materials can bring substantial improvement in various applications other than electronics, from advanced sensors to more efficient catalysts.
The overall objective of the project is to develop novel device concept, demonstrate new or improved functionality of graphene and other 2D materials through the nanoscale and atomic level engineering of their structure.
We have designed a new Scanning Tunneling Microscope (STM) setup with a custom designed state-of-the-art optical access to enable the location of nanoscale structures, as well as the atomic scale imaging and tunneling spectroscopy of graphene and other 2D materials and their nanostructures with the capability of spin-polarized measurements.
We have developed a novel device concept based on zigzag graphene nanoribbons with spin-polarized edges that enables the control of both charge and spin signals using a single back-gate electrode in the simplest three-terminal field effect transistor configuration.
Besides graphene, we also have demonstrated that the atomic level modification of 2D MoS2 crystals through the substitution of single S atoms by oxygen can give rise to novel material properties. We have shown that such a peculiar oxygen substitution reaction can spontaneously occur under ambient conditions, and the resulting oxygen substitution sites act as single atomic catalytic centers substantially improving the catalytic activity of MoS2 single layers for the hydrogen evolution reaction.
We have demonstrated the efficient strain engineering of the bandgap of 2D MoS2 single layers by investigating nanometer scale MoS2 bubbles. We could provide unambiguous evidence for the occurrence of the direct to indirect bandgap transition in MoS2 single layers upon 2% biaxial tensile strain, by measuring a smaller electronic bandgap (tunneling spectroscopy) than the optical gap (photoluminescence).
We have developed a novel Atomic Force Microscope based nanofabrication technique that enables patterning graphene nanostructures on insulating substrates, enabling the AFM based fabrication of graphene nanostructures with lateral size below 10 nm, and high edge quality. This has been achieved by the direct mechanical cutting of graphene by the AFM tip along its high symmetry crystallographic directions.
We have integrated the graphene nanoscale constrictions fabricated by our AFM lithography technique into nanoelectronics devices revealing an unprecedentedly robust quantum point contact operation achieved with graphene, displaying well-defined quantized conductance plateaus down to small quantum numbers, in the absence of a magnetic field, even on standard SiO2/Si substrates , and up to 40K temperatures.
We have synthesized 2D MoSe2 crystals with a high density of Mo vacancies identified by tunneling microscopy and spectroscopy measurements. Theoretical calculations in excellent agreement with the experimental data predict that such defects possess a magnetic moment that can be tuned between 0 and 5 Bohr magnetrons by tuning the Fermi level of the MoSe2 sheet. This way a fully electrical control of the resulting magnetic moment can be achieved.
We have developed a novel nanoengineering technique of graphene, based on inducing nanoscale corrugations of high aspect ratio, allowing the edge-free confinement of its charge carriers. This has enabled the confinement of graphene plasmons into sub-5nm areas, tuning up their resonance frequency into the commercially relevant visible range.
We have provided experimental evidence that the ground state of relatively thick (> 8 layers) ABC graphite samples consists of competing antiferromagnetic and correlated paramagnetic states
We have developed a novel device concept based on zigzag graphene nanoribbons with spin-polarized edges that enables the control of both charge and spin signals using a single back-gate electrode in the simplest three-terminal field effect transistor configuration.
Besides graphene, we also have demonstrated that the atomic level modification of 2D MoS2 crystals through the substitution of single S atoms by oxygen can give rise to novel material properties. We have shown that such a peculiar oxygen substitution reaction can spontaneously occur under ambient conditions, and the resulting oxygen substitution sites act as single atomic catalytic centers substantially improving the catalytic activity of MoS2 single layers for the hydrogen evolution reaction.
We have demonstrated the efficient strain engineering of the bandgap of 2D MoS2 single layers by investigating nanometer scale MoS2 bubbles. We could provide unambiguous evidence for the occurrence of the direct to indirect bandgap transition in MoS2 single layers upon 2% biaxial tensile strain, by measuring a smaller electronic bandgap (tunneling spectroscopy) than the optical gap (photoluminescence).
We have developed a novel Atomic Force Microscope based nanofabrication technique that enables patterning graphene nanostructures on insulating substrates, enabling the AFM based fabrication of graphene nanostructures with lateral size below 10 nm, and high edge quality. This has been achieved by the direct mechanical cutting of graphene by the AFM tip along its high symmetry crystallographic directions.
We have integrated the graphene nanoscale constrictions fabricated by our AFM lithography technique into nanoelectronics devices revealing an unprecedentedly robust quantum point contact operation achieved with graphene, displaying well-defined quantized conductance plateaus down to small quantum numbers, in the absence of a magnetic field, even on standard SiO2/Si substrates , and up to 40K temperatures.
We have synthesized 2D MoSe2 crystals with a high density of Mo vacancies identified by tunneling microscopy and spectroscopy measurements. Theoretical calculations in excellent agreement with the experimental data predict that such defects possess a magnetic moment that can be tuned between 0 and 5 Bohr magnetrons by tuning the Fermi level of the MoSe2 sheet. This way a fully electrical control of the resulting magnetic moment can be achieved.
We have developed a novel nanoengineering technique of graphene, based on inducing nanoscale corrugations of high aspect ratio, allowing the edge-free confinement of its charge carriers. This has enabled the confinement of graphene plasmons into sub-5nm areas, tuning up their resonance frequency into the commercially relevant visible range.
We have provided experimental evidence that the ground state of relatively thick (> 8 layers) ABC graphite samples consists of competing antiferromagnetic and correlated paramagnetic states
- The Scanning Tunneling Microscope system custom designed for the objectives of this project enables us to fully explore the local electronic structure of 2D materials and their nanostructures and to directly detect the magnetic moments emerging in such nanostructures and their atomic scale defects.
- Our novel device concepts developed based on zigzag graphene nanoribbons with edge magnetism goes beyond the state of the art by enabling an efficient control of both charge and spin signal in a device configuration without the need of external magnetic fields or complex side gate electrode systems. This makes much easier its realization as well as subsequent integration.
- We have developed a novel nanofabrication technique for graphene on insulating substrates based on Atomic Force Microscope (AFM). We have achieved significantly higher precision (sub - 10 nm) and higher edge quality than previously, by mechanical cutting of graphene with an AFM tip along its high symmetry crystallographic directions. As-defined graphene nanoconstrictions were integrated into electronic devices demonstrating the most robust graphene based quantum point contact (QPC) operation even on standard SiO2/Si substrates, and up to 40K temperatures.
- We have also demonstrated that the atomic level modification of 2D MoS2 crystals through the substitution of single S atoms by oxygen can give rise to novel material properties. We have shown that such a peculiar oxygen substitution reaction can spontaneously proceed under ambient conditions on months-long time scale. Most importantly we found that the resulting oxygen substitution sites act as single-atomic catalytic centers substantially improving the catalytic activity of MoS2 single layers for the hydrogen evolution reaction. This is an eloquent example how the single-atom level modification of materials enables new properties and opens up new routes for applications
- We were able to realise for the first time visible frequency graphene plasmons through engineering graphene nanocorrugations enabling the low-loss confinement of graphene plasmons in to sub-5nm areas. We have demonstrated that visible graphene plasmons enable a huge Raman enhancement of nearby molecules. We were able to detect phthalocyanine molecules from femto-molar solutions, and even ambient air.
- We have shown experimentally that the ground state of relatively thick (> 8 layer) ABC graphite crystals are competing antiferromagnetic and correlated paramagnetic states. We found that a ferromagnetic state can be induced upon doping, breaking the translation symmetry of the wave function.
- Our novel device concepts developed based on zigzag graphene nanoribbons with edge magnetism goes beyond the state of the art by enabling an efficient control of both charge and spin signal in a device configuration without the need of external magnetic fields or complex side gate electrode systems. This makes much easier its realization as well as subsequent integration.
- We have developed a novel nanofabrication technique for graphene on insulating substrates based on Atomic Force Microscope (AFM). We have achieved significantly higher precision (sub - 10 nm) and higher edge quality than previously, by mechanical cutting of graphene with an AFM tip along its high symmetry crystallographic directions. As-defined graphene nanoconstrictions were integrated into electronic devices demonstrating the most robust graphene based quantum point contact (QPC) operation even on standard SiO2/Si substrates, and up to 40K temperatures.
- We have also demonstrated that the atomic level modification of 2D MoS2 crystals through the substitution of single S atoms by oxygen can give rise to novel material properties. We have shown that such a peculiar oxygen substitution reaction can spontaneously proceed under ambient conditions on months-long time scale. Most importantly we found that the resulting oxygen substitution sites act as single-atomic catalytic centers substantially improving the catalytic activity of MoS2 single layers for the hydrogen evolution reaction. This is an eloquent example how the single-atom level modification of materials enables new properties and opens up new routes for applications
- We were able to realise for the first time visible frequency graphene plasmons through engineering graphene nanocorrugations enabling the low-loss confinement of graphene plasmons in to sub-5nm areas. We have demonstrated that visible graphene plasmons enable a huge Raman enhancement of nearby molecules. We were able to detect phthalocyanine molecules from femto-molar solutions, and even ambient air.
- We have shown experimentally that the ground state of relatively thick (> 8 layer) ABC graphite crystals are competing antiferromagnetic and correlated paramagnetic states. We found that a ferromagnetic state can be induced upon doping, breaking the translation symmetry of the wave function.